1. Technical Field
The present invention generally relates to photographic and video imaging techniques and, more particularly, to a method of producing true color infrared photographic and video images.
2. Discussion
Photographic and video equipment are widely used by law enforcement personnel for surveillance purposes. During the daytime, or under similar bright-light conditions, such photographic and video surveillance is used not only to track subjects, but also for subject identification purposes. This is possible due to the clarity of the image produced by the photographic and/or video equipment.
Surveillance during nighttime or other low-light conditions is more challenging. Due to the low level of ambient light, conventional visible photographic and video imaging is impossible. Such equipment is simply not sensitive enough to capture images during such low light conditions. Recently, however, a new nighttime surveillance technique has been employed by law enforcement officials with success.
To track subjects under low light conditions, law enforcement personnel are now widely employing infrared sensitive equipment. Infrared imaging is based on sensing thermal radiation from a scene and imaging involves recording the heat patterns from the scene. While such infrared sensitive equipment has enabled law enforcement personnel to track subjects during low light conditions, it has not been very useful for subject identification purposes. That is, the image produced by the infrared sensitive equipment is not detailed enough to permit recognition of the facial features of a subject under surveillance. As such, positive identification of a subject is still not possible.
A prior art technique for attempting to overcome the limitations of prior art infrared surveillance techniques is known as false color imaging. Images captured during false color imaging are created from a wider range spectrum than the human visual system can sense. The resulting image is remapped into the visual spectrum to create a pseudo-colored image.
Unfortunately, false color imaging equipment is highly sensitive to blue radiation. This requires the use of a yellow filter to filter out the blue radiation. Such yellow filters distort the color in the image finally produced. Further, the illumination wavelength used for creating red images in such false color imaging equipment is extended into the near infrared spectrum. As such, non-red items that have a high infrared reflectance, such as leaves, are reproduced as red images. Due to these drawbacks, false color imaging has not had great acceptance or success when applied to subjects for identification purposes. Other applications include stealthy surveillance, MPEG-4 object segmentation algorithms, lighting options for the film recording and camcorder industries, and the medical industry.
In view of the foregoing, it would be desirable to provide a technique for producing images during low-light conditions which enables not only tracking of a subject but also sufficient detail to enable subject recognition and identification.
The above and other objects are provided by a method for creating a true color representation of an infrared image. The methodology begins by capturing an infrared image of a scene under surveillance. The captured image of the same scene taken from different infrared spectral bands are then analyzed to determine if an object, such as a face, is identifiable within the image. If an object is identifiable within the image, the methodology compares the object characteristics with a plurality of stored object images. If a match is made, the methodology looks up characteristics of the object in a database and colors the object according to the database information. If no match is made and the true color cannot be identified, or if no object is identifiable within the image, the methodology determines whether a pattern, such as clothing, is identifiable within the image. If a pattern is identifiable within the image, the methodology looks up information regarding the characteristics of the pattern in the database. The pattern is then colored using infrared reflectance characterization from multispectral imaging as guided by the database pattern information. The non-pattern/non-object containing portions of the image are colored using infrared reflectance characterization from multispectral imaging. Though images are measured in the infrared, the multispectral characterization database allows true visible color images to be produced from infrared images. As such, a true color image is produced enabling subject recognition and identification.